Mengfang Chen

Biochar supported nanoscale zerovalent iron composite used as persulfate activator for removing trichloroethylene

Biochar (BC) supported nanoscale zerovalent iron (nZVI) composite was synthesized and used as an activator for persulfate to enhance the trichloroethylene (TCE) removal in aqueous solutions. The degradation efficiency of TCE (0.15mmolL(-1)) was 99.4% in the presence of nZVI/BC (4.5mmolL(-1), nZVI to BC mass ratio was 1:5) and persulfate (4.5mmolL(-1)) within 5min, which was significantly higher than that (56.6%) in nZVI-persulfate system under the same conditions. Owing to large specific surface area and oxygen-containing functional groups of BC, nZVI/BC enhanced the SO4(-) generation and accelerated TCE degradation. On the basis of the characterization and analysis data, possible activation mechanisms of the Fe(2+)/Fe(3+) (Fe(II)/Fe(III)) redox action and the electron-transfer mediator of the BC oxygen functional groups promoting the generation of SO4(-) in nZVI/BC-persulfate system were clarified.

Progress in the preparation and application of modified biochar for improved contaminant removal from water and wastewater

Modified biochar (BC) is reviewed in its preparation, functionality, applications and regeneration. The nature of precursor materials, preparatory conditions and modification methods are key factors influencing BC properties. Steam activation is unsuitable for improving BC surface functionality compared with chemical modifications. Alkali-treated BC possesses the highest surface functionality. Both alkali modified BC and nanomaterial impregnated BC composites are highly favorable for enhancing the adsorption of different contaminants from wastewater. Acidic treatment provides more oxygenated functional groups on BC surfaces. The Langmuir isotherm model provides the best fit for sorption equilibria of heavy metals and anionic contaminants, while the Freundlich isotherm model is the best fit for emerging contaminants. The pseudo 2(nd) order is the most appropriate model of sorption kinetics for all contaminants. Future research should focus on industry-scale applications and hybrid systems for contaminant removal due to scarcity of data.

Biochar Supported Nanoscale Iron Particles for the Efficient Removal of Methyl Orange Dye in Aqueous Solutions

The presence of organic contaminants in industrial effluents is an environmental concern of increasing global importance. One innovative technology for treating contaminated industrial effluents is nanoscale zero-valent iron supported on biochar (nZVI/BC). Based on Transmission Electron Microscopy, X-Ray Diffraction, and Brunauer-Emmett-Teller characterizations, the nZVI was well dispersed on the biochar and aggregation was dramatically reduced. Methyl orange (MO) served as the representative organic contaminant for verifying the effectiveness of the composite. Using decolorization efficiency as an indicator of treatment effectiveness, increasing doses of nZVI/BC yielded progressively better results with 98.51% of MO decolorized by 0.6 g/L of composite at an nZVI/BC mass ratio of 1:5. The superior decolorization efficiency of the nZVI/BC was attributed to the increase in the dispersion and reactivity of nZVI while biochar increasing the contact area with contaminant and the adsorption of composites. Additionally, the buffering function of acid-washed biochar could be in favor of maintaining the reactivity of nZVI. Furthermore, the aging nZVI/BC for 30 day was able to maintain the removal efficiency indicating that the oxidation of nZVI may be delayed in the presence of biochar. Therefore, the composite of nZVI/BC could represent an effective functional material for treating wastewater containing organic dyes in the future.

Determination of low levels of polycyclic aromatic hydrocarbons in soil by high performance liquid chromatography with tandem fluorescence and diode-array detectors

Risk assessment of polycyclic aromatic hydrocarbons (PAHs) contaminated soil and source apportionment require accurate analysis of the concentration of each PAH congener in the soil. However, determination of low level PAH congeners in soil is difficult because of similarity in the chemical properties of 16 PAHs and severe matrix interferences due to complex composition of soils. It is therefore imperative to develop a sensitive and accurate method for determination of low level PAHs in soil. In this work, high performance liquid chromatography equipped with fluorescence and diode-array detectors (HPLC-FLD-DAD) was used to determine the concentration of 16 PAHs in soil. The separation of the 16 PAHs was achieved by optimization of the mobile phase gradient elution program and FLD wavelength switching program. Qualitative analysis of the 16 PAHs was based on the retention time (RT) and each PAH specific spectrum obtained from DAD. In contrast, the quantitative analysis of individual PAH congeners was based on the peak areas at the specific wavelength with DAD and FLD. Under optimal conditions the detection limit was in the range 1.0-9.5 μg L(-1) for 16 PAHs with DAD and 0.01-0.1 μg L(-1) for 15 PAHs with FLD, and the RSD of PAHs was less than 5% with DAD and 3% with FLD. The spiked recoveries were in the range 61-96%, with the exception of NaP (<40%). The results show that HPLC-FLD-DAD can provide more accurate and reliable analysis of low level PAH congeners in soil samples.

Isolation, identification and characterization of Bacillus amyloliquefaciens BZ-6, a bacterial isolate for enhancing oil recovery from oily sludge

Over 100 biosurfactant-producing microorganisms were isolated from oily sludge and petroleum-contaminated soil from Shengli oil field in north China. Sixteen of the bacterial isolates produced biosurfactants and reduced the surface tension of the growth medium from 71 to <30 mN m(-1) after 72 h of growth. These bacteria were used to treat oily sludge and the recovery efficiencies of oil from oily sludge were determined. The oil recovery efficiencies of different isolates ranged from 39% to 88%. Bacterial isolate BZ-6 was found to be the most efficient strain and the three phases (oil, water and sediment) were separated automatically after the sludge was treated with the culture medium of BZ-6. Based on morphological, physiological characteristics and molecular identification, isolate BZ-6 was identified as Bacillus amyloliquefaciens. The biosurfactant produced by isolate BZ-6 was purified and analyzed by high performance liquid chromatography-electrospray ionization tandem mass spectrometry. There were four ion peaks representing four different fengycin A homologues.

Heterogeneously catalyzed persulfate with a CuMgFe layered double hydroxide for the degradation of ethylbenzene

CuMgFe layered double hydroxide (CuMgFe-LDH) was successfully synthesized and characterized as an efficient catalyst of persulfate (PS) for the degradation of ethylbenzene. Under the conditions of 0.2gL-1 CuMgFe-LDH and 4.0mmolL-1 persulfate at pH 7.6, the degradation efficiency of 0.08mmolL-1 ethylbenzene was 93.7% with TOC removal efficiency of 65.2% in 24h, and the concentration of Cu leached into the solution was as low as 0.095mgL-1 after the reaction. The reuse of CuMgFe-LDH showed that the catalyst was highly stable after 5 recycles. Electron Spin Resonance (ESR) test and free radical quenching experiment indicated that SO4- and OH radicals were the dominant species accounted for the degradation of ethylbenzene in the CuMgFe-LDH/persulfate system. Catalytic mechanism of the formation of a complex of Cu(II)O3SOOSO32- and the subsequent redox cycle of Cu(II)/Cu(III) accounted for the generation of radicals was proposed.

Novel Alleviation Mechanisms of Aluminum Phytotoxicity via Released Biosilicon from Rice Straw-Derived Biochars.

Replacing biosilicon and biocarbon in soil via biochar amendment is a novel approach for soil amelioration and pollution remediation. The unique roles of silicon (Si)-rich biochar in aluminum (Al) phytotoxicity alleviation have not been discovered. In this study, the alleviation of Al phytotoxicity to wheat plants (root tips cell death) by biochars fabricated from rice straw pyrolyzed at 400 and 700 °C (RS400 and RS700) and the feedstock (RS100) were studied using a slurry system containing typical acidic soils for a 15-day exposure experiment. The distributions of Al and Si in the slurry solution, soil and plant root tissue were monitored by staining methods, chemical extractions and SEM-EDS observations. We found that the biological sourced silicon in biochars served dual roles in Al phytotoxicity alleviation in acidic soil slurry. On one hand, the Si particles reduced the amount of soil exchangeable Al and prevented the migration of Al to the plant. More importantly, the Si released from biochars synchronously absorbed by the plants and coordinated with Al to form Al-Si compounds in the epidermis of wheat roots, which is a new mechanism for Al phytotoxicity alleviation in acidic soil slurry by biochar amendment. In addition, the steady release of Si from the rice straw-derived biochars was a sustainable Si source for aluminosilicate reconstruction in acidic soil.

Assessment of Human Health Risk for an Area Impacted by a Large-Scale Metallurgical Refinery Complex in Hunan, China

ABSTRACT Due to accelerated urbanization and reform of industrial structure in China, polluting industries in major cities have been closed or relocated. Consequently, large numbers of industrial sites were generated and the contaminated soils on and around these sites may pose risks to humans. This case study presents an estimation of human health risks for an area that is mainly impacted through air dispersion and deposition from a large-scale metallurgical refinery complex in Zhuzhou city, Hunan Province, China. Carcinogenic and non-carcinogenic risks posed by the contaminants were estimated under future industrial and residential land use scenarios. The result shows that adverse health effects may occur primarily through ingestion of soils contaminated with As, Cd, and Pb. The total carcinogenic risks of multiple contaminants for a large area exceed the acceptable risk level of 1 × 10−5, and several localized hotspots, where the total hazard index exceeds 1 were identified. Soils in the Tongda site pose the highest carcinogenic risks and non-carcinogenic hazards. It is concluded that potential human health risks exist under the proposed redevelopment scenarios, and development of risk-based remediation strategies is recommended.

Lead adsorption by biochar under the elevated competition of cadmium and aluminum

Competitive adsorption studies are important to accurately estimate the lead adsorption capacity on biochar in soil. The structure of biochars was evaluated by Fourier-Transform Infrared Spectroscopy and X-ray Diffraction, and the competitive of Cadmium (Cd) and Aluminum (Al) with Lead (Pb) adsorption were determined by kinetic experiments and pH effects. Adsorption kinetics indicated that the adsorption amount (mg g−1) of Pb by biochar was in the decreasing order of CM400 (90.9) > BB600 (56.5) > CM100 (29.2), the presence of the oxygen-containing functional groups, Si-containing mineral, PO43− and CO32− significantly contributed to Pb adsorption by biochars. With the presence of Cd, Pb adsorption amount was reduced by 42.6%, 23.7% and 19.3% for CM100, CM400 and BB600, respectively. The Si-containing mineral, PO43− and CO32− that were rich in CM400 and BB600 has led to less competition by Cd. In addition, Al showed a strong competition with Pb leading to the adsorption being reduced by 95.8%, 82.3% and 80.6%, respectively for CM100, CM400 and BB600. This was mainly attributed to the additional acidification effect by Al resulting in a counteractive of biochar’s liming effect. Results from this study are important for accurately estimating the heavy metal adsorption by biochar in soil.

Enhanced Fenton-like Degradation of Trichloroethylene by Hydrogen Peroxide Activated with Nanoscale Zero Valent Iron Loaded on Biochar

Composite of nanoscale Zero Valent Iron (nZVI) loaded on Biochar (BC) was prepared and characterized as hydrogen peroxide (H2O2) activator for the degradation of trichloroethylene (TCE). nZVI is homogeneously loaded on lamellarly structured BC surfaces to form nZVI/BC with specific surface area (SBET) of 184.91 m2 g−1, which can efficiently activate H2O2 to achieve TCE degradation efficiency of 98.9% with TOC removal of 78.2% within 30 min under the conditions of 0.10 mmol L−1 TCE, 1.13 g L−1 nZVI/BC and 1.50 mmol L−1 H2O2. Test results from the Electron Spin Resonance (ESR) measurement and coumarin based fluorescent probe technology indicated that ∙OH radicals were the dominant species responsible for the degradation of TCE within the nZVI/BC-H2O2 system. Activation mechanism of the redox action of Fe2+/Fe3+ generated under both aerobic and anaerobic conditions from nZVI and single electron transfer process from BC surface bound C–OH to H2O2 promoted decomposition of H2O2 into ∙OH radicals was proposed.